Air conveyors are commonly used to convey empty plastic bottles. The bottles are supported by a ring flange located between the containers' shoulder and the threaded part of the container's neck. The flange rests on a pair of opposing guides which in turn define a guideway along which the bottle neck can move. Air is blown in the direction in which the bottles are to be conveyed, usually at the level of the neck, less commonly on the bottle's body. This type of conveyor eliminates the problems associated with container stability. Another advantage is the high speed at which the bottles may be conveyed.
Prior art air conveyor systems disclose rigid curve sections where the guides follow a smooth curve. One drawback of such prior art devices arises when bottles with different neck diameters need to be conveyed on the same conveyor. The spacing of the guides supporting the neck ring must then be changed, which it is desirable to do automatically, usually via the use of remotely controlled pistons, solenoids, or the like. While it is fairly straightforward to move straight and parallel guide sections in and out to adjust the distance between them, doing the same in curved sections is not as simple as it is not only the guide's position that must change, but also its shape. Indeed, if the distance between two curved guides is to be constant along their length, these guides need to be concentric. In other words, they must both be curved about a common centre of curvature, and each one's radius of curvature must be proportional to its distance from this point.
Prior art devices have addressed the above drawbacks by providing for a curved neck guide fabricated from a pair of slightly flexible curved segments, each segment attached to a pair of pistons rods. The piston rods move the segment outwards or inwards thereby causing a corresponding increase or decrease in the radius of curvature. In order to compensate for the increase or decrease in the radius of curvature, each segment is flexed slightly due to small differences in the length of travel of the piston rods. The problem of gaps which arise between adjacent segments due to an increase in curvature has been addressed in such prior art devices by inserting, using an additional actuating piston, a very small curve segment into the gap.
One drawback of the above prior-art devices is that they move only between two positions and therefore provide only for a small number of different guideway widths.
One challenge is therefore to move a curved guide section toward or away from its centre of curvature while at the same time adjusting its radius of curvature so that the guide's centre of curvature remains stationary. This guarantees that parallelism is maintained between the two curved guide sections that support the bottles, thereby preventing the bottles from either jamming or escaping the guideway at any point along the curve.